mtd: cfi_cmdset_*: kill useless 'ret' variable initializers

The 'ret' local variables are typically initialized to 0 but this value is
often unused, thus we can kill those initializers.

Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>