staging: vt6656: Refactor the vnt_set_bss_mode function

staging: vt6656: Refactor the vnt_set_bss_mode function

Remove all the duplicate code in the "if, else if, else" statements as
all the branches in every "if" are almost the same. The only difference
between branches is some value. So, use variables instead of repeat
code.

Also, remove the unnecessary casting to u8 type because the
"priv->bb_type" variable is already an u8 tpe.

Signed-off-by: Oscar Carter <oscar.carter@gmx.com>
Link: https://lore.kernel.org/r/20200429152307.5871-3-oscar.carter@gmx.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>