staging: fbtft: fix out of bound access

str was 16 bytes but was mentioned as 128 in snprintf.
again msg is 128 bytes but not sufficient to hold the complete debug
message of register values.
Now removed the use of str, msg and print the register values from the
loop.

Signed-off-by: Sudip Mukherjee <sudip@vectorindia.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>