mhi: core: Fix undefined reference to `__bad_udelay'

According to the comment in arch/arm/include/asm/delay.h,
__bad_udelay is specifically designed on ARM to produce a
build failure when udelay is called with a value > 2000.
Fix the issue by using mdelay for value > 2000.

Change-Id: Ia5ee988eeef68ce60b637232e0dd3989b8cbfe64
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>