data_chr/data.c: Fixed checkpatch.pl warnings

Fixed checkpatch.pl warnings:

  - pr_warn instead of printk(KERN_WARNING

  - over long line with 8 space tabs

  - space after ','
data_ioctl/data.c: Fixed checkpatch.pl warnings

Fixed checkpatch.pl warnings:

  - pr_warn instead of printk(KERN_WARNING

  - over long line with 8 space tabs

  - switch statement indentation

  - // C99 comments

  - const struct file_operations

  - missing space after ','
data_rw/data.c: Fixed checkpatch.pl warnings

Fixed checkpatch.pl warnings:

  - pr_warn instead of printk(KERN_WARNING

  - over long line with 8 space tabs

  - // C99 comments

  - const struct file_operations

  - missing space after ','

  - "foo* bar" should be "foo *bar"

  - braces not necessary for single statement blocks
replaced printk with pr_ equivalent

Replaced all instances of printk with their pr_ equivalent version.
These would have been noticed by checkpatch.pl.
data_sk/data.c: Fixed checkpatch.pl warnings

Fixed checkpatch.pl warnings:

  - // C99 comments

  - braces not necessary for single statement blocks

  - case statement indentation

  - const struct file_operations

  - over long line with 8 space tabs

  - missing space after ','

  - "foo* bar" should be "foo *bar"
fifo_fix/fifo.c: Fixed checkpatch.pl warnings

Fixed checkpatch.pl warnings:

  - // C99 comments

  - braces not necessary for single statement blocks

  - do not initialize statics to zero

  - { on next line for function definitions

  - const struct file_operations

  - over long line with 8 space tabs

  - missing space after ','

  - "foo* bar" should be "foo *bar"