libc: fix setting return value and errno in fallocate()

libc: fix setting return value and errno in fallocate()

fallocate system call must return 0 on success. On error, -1 is returned
and errno is set to indicate the error.

However there is an error in fallocate which is fixed by this patch - it
does not set errno and returns invalid value on error (it returns error
code instead of -1).

This error is detected in LTP's test kernel/syscalls/fallocate02:

    ----------->8----------
    fallocate(..., 1, 0, 1024) failed, expected errno:9: TEST_ERRNO=0
    fallocate(..., 1, -1024, 1024) failed, expected errno:22: TEST_ERRNO=0
    fallocate(..., 1, 1024, -1024) failed, expected errno:22: TEST_ERRNO=0
    fallocate(..., 1, 12288, 0) failed, expected errno:22: TEST_ERRNO=0
    fallocate(..., 1, 12288, -1024) failed, expected errno:22: TEST_ERRNO=0
    fallocate(..., 1, -24576, 1024) failed, expected errno:22: TEST_ERRNO=0
    ----------->8----------

Signed-off-by: Yuriy Kolerov <yuriy.kolerov@synopsys.com>