mtd: tests: rename sources in order to link a helper object

Each mtd test module have a single source whose name is the same as
the module name. In order to link a single object including helper
functions to every test module, this rename these sources to the
different names.

Signed-off-by: Akinobu Mita <[e-mail]>
Cc: Brian Norris <[e-mail]>
Cc: Vikram Narayanan <[e-mail]>
Cc: Adrian Hunter <[e-mail]>
Signed-off-by: Artem Bityutskiy <[e-mail]>
Signed-off-by: David Woodhouse <[e-mail]>

drivers/mtd/tests/Makefile

···
 obj-$(CONFIG_MTD_TESTS) += mtd_torturetest.o
 obj-$(CONFIG_MTD_TESTS) += mtd_nandecctest.o
 obj-$(CONFIG_MTD_TESTS) += mtd_nandbiterrs.o
+
+mtd_oobtest-objs := oobtest.o mtd_test.o
+mtd_pagetest-objs := pagetest.o mtd_test.o
+mtd_readtest-objs := readtest.o mtd_test.o
+mtd_speedtest-objs := speedtest.o mtd_test.o
+mtd_stresstest-objs := stresstest.o mtd_test.o
+mtd_subpagetest-objs := subpagetest.o mtd_test.o
+mtd_torturetest-objs := torturetest.o mtd_test.o
+mtd_nandbiterrs-objs := nandbiterrs.o mtd_test.o