musb_host: factor out musb_ep_{get|set}_qh()

Factor out the often used code to get/set the active 'qh'
pointer for the hardware endpoint.  Change the way the case
of a shared FIFO is handled by setting *both* 'in_qh' and
'out_qh' fields of 'struct musb_hw_ep'.  That seems more
consistent and makes getting to the current 'qh' easy when
the code knows the direction beforehand.

While at it, turn some assignments into intializers and
fix declaration style in the vicinity.

Signed-off-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>