media: dvb_ca_en50221: Avoid assignments in ifs

Fixed all:
  ERROR: do not use assignment in if condition

Fixed also "-strict" checks in this patch:
- Changed "if (ret != 0)" to "if (ret)".
- Camel case variables have been converted to kernel_case.
- Comparison to NULL written as "!<var>".
- No space is necessary after a cast.
Signed-off-by: Jasmin Jessich <jasmin@anw.at>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>