realtek_mst_i2c_spi.c: Fix cmd timeout issue

Chip erasures take much longer than sector and bank
erasures. Allow the wait loop helper to multiply the
max timeout in this very specific case while quickly
timeout for other ops that are expected to be shorter.

V.2: Fix nonsense fall though warn-err

BUG=b:152558985,b:148745673
BRANCH=none
TEST=flashrom -p realtek_mst_i2c_spi:bus=8 -E &&
     flashrom -p realtek_mst_i2c_spi:bus=8 -w foo
    (cycle)..

Change-Id: I4a36aa3101827e69eb244775d25bbb476d4bb780
Signed-off-by: Edward O'Callaghan <quasisec@google.com>
Reviewed-on: https://review.coreboot.org/c/flashrom/+/41123


Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Sam McNally <sammc@google.com>