ABI: sysfs-devices-removable: make a table valid as ReST markup

Changeset 70f400d4 ("driver core: Move the "removable" attribute from USB to core")
added a table to the file, but not using a valid ReST format.

Change it to avoid build issues when producing documentation with
"make htmldocs".

Fixes: 70f400d4 ("driver core: Move the "removable" attribute from USB to core")
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/bf83354747b8abaa486fe03af4be2826363469cb.1632740376.git.mchehab+huawei@kernel.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/ABI/testing/sysfs-devices-removable

@@ -7,10 +7,12 @@ Description:
 		bus / platform-specific way. This attribute is only present for
 		devices that can support determining such information:
 
-		"removable": device can be removed from the platform by the user
-		"fixed":     device is fixed to the platform / cannot be removed
+		===========  ===================================================
+		"removable"  device can be removed from the platform by the user
+		"fixed"      device is fixed to the platform / cannot be removed
 			     by the user.
-		"unknown":   The information is unavailable / cannot be deduced.
+		"unknown"    The information is unavailable / cannot be deduced.
+		===========  ===================================================
 
 		Currently this is only supported by USB (which infers the
 		information from a combination of hub descriptor bits and