uio_find_by_uio_name: return NULL if no matching device was found

uio_find_by_uio_name() returned the last found device instead of NULL if no
matching device was found. Use a temporary variable for searching.

Signed-off-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
Signed-off-by: Benedikt Spranger <b.spranger@linutronix.de>
Add accessor function for uio file descriptor

In earlier versions of libuio, interrupt handling routines had to be written
by the application. They have used the fd field in the uio structure to select
or poll on one or more file descriptors, associated with one or more
interrupts.

Later versions of libuio stopped exposing the fields of the uio structure
directly, and introduced accessor functions for the fields that
applications could use. Additionally, a helper function uio_irqwait() was
introduced to allow handling one interrupt without application complexity.

To handle many low-occurence interrupts it is desirable to handle them all
in one poll/select loop. Add an accessor function to obtain the fd field, to
satisfy this use case.

Signed-off-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
Signed-off-by: Benedikt Spranger <b.spranger@linutronix.de>
rename .texinfo files

The use of '.texinfo' for Texinfo files is discouraged; use '.texi' instead.

Signed-off-by: Benedikt Spranger <b.spranger@linutronix.de>
v0.2.6

Signed-off-by: Benedikt Spranger <b.spranger@linutronix.de>