ACPI: thinkpad-acpi: trivial fix to documentation

Fix a stray ibm-acpi that should have been replaced with thinkpad-acpi.
Thanks to Damjan <gdamjan@mail.net.mk> for noticing this one.
Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Signed-off-by: Len Brown <len.brown@intel.com>

Documentation/laptops/thinkpad-acpi.txt

@@ -1309,7 +1309,7 @@ Enabling debugging output
 The module takes a debug parameter which can be used to selectively
 enable various classes of debugging output, for example:
 
-	 modprobe ibm_acpi debug=0xffff
+	 modprobe thinkpad_acpi debug=0xffff
 
 will enable all debugging output classes.  It takes a bitmask, so
 to enable more than one output class, just add their values.