dm ioctl: drop always-false condition

The expression 'indata[3] > ULONG_MAX' always evaluates to false since
indata[] is declared as an array of *unsigned long* elements and #define
ULONG_MAX represents the max value of that exact type...

Note that gcc seems to be able to detect the dead code here and eliminate
this check anyway...

Found by Linux Verification Center (linuxtesting.org) with the SVACE static
analysis tool.

Signed-off-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Reviewed-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>