igb: Fix lack of flush after register write and before delay
igb: Fix lack of flush after register write and before delay

Register writes followed by a delay are required to have a flush
before the delay in order to commit the values to the register.  Without
the flush, the code following the delay may not function correctly.

Reported-by: Tong Ho <b7a0b246340a425c3d6a76f5e3e9fdca65f544cd@ericsson.com>
Reported-by: Guenter Roeck <32ce62c5480002985aec58d7044038218061ef55@ericsson.com>
Signed-off-by: Carolyn Wyborny <e35dd5c02b168c490ac58c3994dfe3c4e0d9fc66@intel.com>
Tested-by:  Aaron Brown <4723df1d9a4136f7b76e1bf6434e33afc91d2139@intel.com>
Signed-off-by: Jeff Kirsher <87e35f5be20bb3e67f4ba6b86f5f6be3085b1b3a@intel.com>

TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs