ima: remove redundant initialization of pointer 'file'.

The pointer 'file' is being initialized with a value that is never read,
it is being re-assigned the same value later on closer to where it is
being first used. The initialization is redundant and can be removed.

Cleans up clang scan build warning:
security/integrity/ima/ima_main.c:434:15: warning: Value stored to 'file'
during its initialization is never read [deadcode.DeadStores]

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>