util: change return value of startswith() to non-const

This way we can use it on non-const strings, and don't end up with a
const'ified result.

This is similar to libc's strstr() which also takes a const string but
returns a non-const one.

Signed-off-by: Anthony G. Basile <blueness@gentoo.org>
util: change return value of startswith() to non-const

This way we can use it on non-const strings, and don't end up with a
const'ified result.

This is similar to libc's strstr() which also takes a const string but
returns a non-const one.

Signed-off-by: Anthony G. Basile <blueness@gentoo.org>