usb: renesas_usbhs: simplify usbhs_status_get_device_state()

Similar to usbhs_status_get_ctrl_stage(), *_get_device_state() is not
supposed to return any error code since its return value is the DVSQ
bitfield of the INTSTS0 register. According to SoC HW manual rev1.00,
every single value of DVSQ[2:0] is valid and none is an error:

----8<----
Device State
000: Powered state
001: Default state
010: Address state
011: Configuration state
1xx: Suspended state
----8<----

Hence, simplify the function body. The motivation behind dropping the
switch/case construct is being able to implement reading the suspended
state. The latter (based on the above DVSQ[2:0] description) doesn't
have a unique value, but is rather a list of states (which makes
switch/case less suitable for reading/validating it):

100: (Suspended) Powered state
101: (Suspended) Default state
110: (Suspended) Address state
111: (Suspended) Configuration state

Signed-off-by: Eugeniu Rosca <erosca@de.adit-jv.com>
Signed-off-by: Veeraiyan Chidambaram <veeraiyan.chidambaram@in.bosch.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>