bcma: change max PCI read request size to 128

This PCIe controller does not support a max read request size above 128
bytes. The sold card I tested this controller with used 128 as default
value, but some new routers are sold with BCM4331 chips, which have a
default max read request size of 512. This device fails at the first
DMA reqeust whch is bigger than 126 bytes.

This patch changes the max read request size to 128 for every device on
the PCIe link.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>