command, log: print with "log show" a full logbuffer

If the logbuffer contains LOGBUFF_LEN chars, they never got
printed with the "log show" command, because chars get
printed with the following for loop:

for (i = 0; i < (size & LOGBUFF_MASK); i++) {

with size = LOGBUFF_LEN and LOGBUFF_MASK = (LOGBUFF_LEN-1)
for loop never executed ...

Fix this.

Signed-off-by: Heiko Schocher <hs@denx.de>
Acked-by: Detlev Zundel <dzu@denx.de>

Fixed merge conflict.
Signed-off-by: Wolfgang Denk <wd@denx.de>