ipw2x00: remove redundant variables len, ret, reason and crypt

Variables len, ret, reason and crypt are assigned values that
are never read, hence they are redundant and can be removed.

Note: For the variable ret, a return code is being assigned, but
this is not returned and 0 is currently being returned, I believe
this is OK.

Cleans up clang warnings:
warning: variable 'len' set but not used [-Wunused-but-set-variable]
variable 'ret' set but not used [-Wunused-but-set-variable]
warning: variable 'reason' set but not used [-Wunused-but-set-variable]
warning: variable 'crypt' set but not used [-Wunused-but-set-variable]

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>